1. Field of the Invention
The present invention relates to a method of discriminating coins, in particular to a method of discriminating coin properties such as a material, diameter and thickness of the coin by using a coin discriminating sensor in the form of a proximity switch.
2. Related Art Statement
There has been known to use a plurality pair of sensor coils for discriminating the material and dimension of the coin in such a manner that sensor coils of the each pair are opposedly arranged on both sides of a coin passage in a coin acceptor so as to detect a variation of an inductance which is generated in the sensor coils by a coin passing through the coin passage when a magnetic field generated by the sensor coils is crossed by the coin.
Hitherto, such a sensor coil used in the aforementioned manner has been generally formed in the form of a circular sensor coil as shown by reference numeral 1 in FIG. 1. However, when three kinds of coins A, B and C of different diameters but the same material cross the magnetic field of the circular sensor coil as shown in FIG. 1, the peak variations of the coil reactance caused by the coins A, B and C occur at the same time position T.sub.1 on a time coordinate axis T as shown by variation curves "a", "b" and "c" in FIG. 2. Accordingly, in the prior method of discriminating a plurality of coins having different diameters by using the sensor coils, the coins are discriminated by only the difference of the peak values of the coil reactance occurred at the same time position T.sub.1 on the time coordinate axis T.
However, if the diameter of a pair of the opposedly arranged circular sensor coils and/or the position of the circular sensor coils relative to a guide rail 2 on which the coins to be discriminated roll between a pair of the sensor coils is not pertinent for all three kinds of coins, the peak variations can not be distinguished from each other as is noted by comparing the variation curves "b" and "c" shown in FIG. 2, resulting in that the coins B and C can not be discriminated by the peak variations. Furthermore, in order to effect the discrimination of the coin diameter by use of the circular sensor coil, materials of coins to be discriminated must be the same and then additional sensor coils are required for discriminating the material of the coin. Accordingly, it is necessary that a pair of material discriminating sensor coils and a pair of diameter discriminating sensor coils are sequently arranged along the coin passage. Furthermore, it is preferable that the center of magnetic bundle of the material discriminating sensor coil coincides with the center of the coin to be discriminated and the center of magnetic bundle of the diameter discriminating sensor coil coincides with the upper end of coin to be discriminated.
The inventor had invented an oval sensor coil as disclosed in Japanese Patent application Laid-Open publication No. 61-289486 (U.S. Pat. No. 4,842,119). The oval sensor coil has an oval configuration in a section parallel to the coin passage, with one end in the longitudinal direction of the oval configuration having a large radius of curvature and the other end in the longitudinal direction of the oval configuration having a small radius of curvature as shown in FIG. 3.
When a magnetic field generated by a pair of the oval sensor coils 3 is crossed by each of coins A, B and C of different diameters as shown in FIG. 3, which rolls on the guide rail 2 extending between the opposedly arranged the oval sensor coils 3, a resonance portion of an L.C. oscillating circuit connected to the oval sensor coil detects variation of the coil reactance caused by variation of "Q" of the sensor coil and variation of leak magnetic bundle as shown in FIG. 4. The peak reactance L.sub.a caused by the small coin A, the peak reactance L.sub.b caused by the middle coin B and the peak reactance L.sub.c caused by the large coin C occur at different time positions T.sub.a, T.sub.b and T.sub.c on the coin detection time axis T, respectively.
Thus, according to the oval sensor coil, a position occurring the peak reactance caused by a coin having a specific diameter can be determined by a clock counter which is started when the variation of the sensor coil reactance caused by the coin begins to occur. Therefore, the discrimination of the materials and dimensions of a plurality of different coins can be accuratelly effected by only a pair of sensor coils since the value of peak reactance occurred at the specific time position for the specific coin diameter is different for the coin material.